Conventionally, there are known various types of variable compression ratio mechanisms arranged to vary a mechanical compression ratio of an internal combustion engine. For example, the present applicant and so on make many proposals of the variable compression ratio mechanisms arranged to vary a geometry of a multi-link piston crank mechanism. Furthermore, there is known a variable compression ratio mechanism arranged to displace a position of the cylinder in the upward and downward directions with respect to a center position of the crank shaft.
On the other hand, there is known a spark ignition internal combustion engine of cylinder direct injection type in which a fuel injection valve is disposed to confront the combustion chamber, and which is arranged to inject the fuel directly to the cylinder. In this internal combustion engine of the cylinder direct injection type, as described in the patent document 1, when homogeneous combustion is performed in particular in the high load region, the fuel injection is performed during the intake process. The fuel injection period which is set in this way during the intake process is a value based on the actual time, and which is proportional to the fuel injection amount. The crank angle becomes larger as it is higher speed and higher load. When the injection rate of the fuel injection valve (the injection amount per the unit time) is small, the fuel injection is not finished until a timing after an intake lower dead center. The evaporation and the mixture of the fuel is deteriorated.
With respect to this problems, the patent document 1 is arranged to provide a deference of the lift characteristics of the pair of the intake valves in the high speed and high load region, so as to generate a swirl. With this, the evaporation of the fuel and the mixture of the fuel are advanced (facilitated).
In this case, the patent document 1 discloses an example in which a fuel injection start timing in the high load region is just set to an exhaust upper dead center (referred also to an intake upper dead center). In a case where the fuel injection is started at the exhaust upper dead center in this way, the injected fuel is impinged and adhered on the piston. This becomes the cause for the generation of the smoke in the high load region. Generally, the fuel injection is started at a timing slightly later than the exhaust upper dead center.
As described in the patent document 1, in a case where the fuel injection end timing is excessively retarded at the high load, it is not possible to ensure the time necessary for the mixture and the evaporation of the fuel spraying, so that the combustion is deteriorated. On the other hand, in a case where the fuel injection start timing is closer to the exhaust upper dead center, the smoke is increased by the collision and the adhesion of the fuel on the piston. Accordingly, it is necessary to ensure the injection rate of the fuel injection valve to the large rate to some extent. However, when the injection rate of the fuel injection valve is large, the injection period (that is, the opening period of the fuel injection valve) becomes excessively short when the fuel injection amount is small. Consequently, the measurement accuracy is decreased.